1. Field of the Invention
The present invention relates to colorants, such as pigments, as well as the use of the colorants in ink and inkjet ink compositions or formulations, as well as methods of forming images using the ink or inkjet ink formulations.
2. Description of the Related Art
An ink or inkjet ink composition generally contains a vehicle, which functions as a carrier, and a colorant such as a dye or pigment. Additives and/or cosolvents can also be incorporated in order to adjust the ink or inkjet ink to attain the desired overall performance properties.
In general, pigments alone are not readily dispersible in liquid vehicles. A variety of techniques have been developed providing stable pigment dispersions that can be used in inkjet printing. For example, dispersants can be added to the pigment to improve its dispersibility in a particular medium. Examples of dispersants include water-soluble polymers and surfactants.
Modified pigments have also been developed which provide ink compositions with improved properties, such as dispersibility, without the need for an external dispersant. For example, U.S. Pat. No. 5,851,280 discloses methods for the attachment of organic groups to pigments including, for example, attachment via a diazonium reaction wherein the organic group is part of the diazonium salt. The resulting surface-modified pigments can be used in a variety of applications, such as inks, inkjet inks, coatings, toners, plastics, rubbers, and the like. These modified pigments provide inkjet inks with good overall properties.
It is always highly desirable for inks, such as inkjet inks, like black inkjet ink, to have very high optical density (OD) on a variety of papers, such as plain papers. Obtaining optical density on a variety of papers can be a challenge considering the variation in quality of papers, such as inkjet papers in the market today. Further, there are a variety of factors that can affect optical density on paper.
Accordingly, a need exists for colorants, like pigments, and ink compositions, such as inkjet compositions, that provide or afford good optical density when an image is created from an ink formulation.